RFID stands for Radio-Frequency IDentification. An RFID transponder, or ‘tag’, serves a similar purpose as a bar code or a magnetic strip on the back of a credit card; it provides an identifier for a particular object, although, unlike a barcode or magnetic strip, some tags support being written to. An RFID system carries data in these tags, and retrieves data from the tags wirelessly. Data within a tag may provide identification for an item in manufacture, goods in transit, a location, the identity of a vehicle, an animal, or an individual. By including additional data, the ability is provided for supporting applications through item-specific information or instructions available upon reading the tag.
A basic RFID system comprises a reader, including an interrogator module (transmitter) and a closely-coupled reader (receiver) module (a transceiver is often used), and a transponder (an RFID tag) electronically programmed with unique identifying information. Both the reader/interrogator and transponder have antennas, which respectively emit and receive radio signals to activate the tag, read data from the tag, and write data to it.
The interrogator module in the reader emits an RF activation signal with a range of anywhere from one inch to 100 feet or more, depending upon the interrogator's power output and the radio frequency used. The RF signal from the interrogator provides power to operate a ‘passive’ tag's integrated circuit or microprocessor and associated memory.
In a tag-read situation, when an RFID tag passes through the electromagnetic zone created by the interrogator (i.e., when the tag is ‘in-field’), it detects the activation signal, upon which the tag conveys its stored data to the reader module, using power provided by the interrogator. The reader decodes the data received from the tag's integrated circuit and the decoded data may be processed by the reader, or passed to another device (e.g., a computer) for processing.
In a tag-write situation, when an RFID tag is ‘in-field’, it detects the interrogator's activation signal, upon which the tag transfers data sent from either the interrogator or the reader module to the tag's internal memory, again using power harvested from the transmit signal to power the tag to process the command and provide a response.
Problem to be Solved
Several problems with previous RFID readers exist, including insufficient sensitivity to signals from RFID tags, and the number of separate circuits required to perform various reader functions including tag signal envelope detection, battery level detection, feedback control of RF power, temperature compensation, and load/backscatter modulation.
All known previous methods need an entire subcircuit comprised of multiple discrete components for each of these functions. Previous methods to improve RFID reader sensitivity also require additional expensive filtering, low-noise amplifiers, costly circulators, and/or multiple antennas.